I have a '91 sport 4x4 with automatic transmission and the 4.0 high output that absolutely will not start. I bought it from a buddy of mine and it has been running for some time. Here is what has been done. New CPS, spark plugs and wires, distributor cap, ignition coil, battery and ASD relay. The vacuum lines seem to be good, the grounds also check out, has fuel pressure and gets spark and good compression. The distributor was never taken off so I don't believe it's out of time. Could it possibly be the computer? Any ideas? I've exhausted every idea up to this point. The motor cranks over but just won't pass the tipping point and just fire up.

 

Try putting jeep in neutral and see if it starts. If it does your Neutral safety switch is bad. Also a bad throttle position sensors will not allow jeep to start

 

I'll have to try checking that throttle position sensor. Thanks for the suggestion. I've never owned a jeep before so some of these issues are new to me. I've tried to start it in neutral before and got nothing.

 

You said spark plugs and wires, you get the firing order right? I know it's a simple thing but people still mess it up.

 

Yeah the firing order is right

 

just stopped running or worked on and now wont start ?

 

I'm not entirely sure the history of why it stopped running other than it was parked and wouldn't start again. My buddy said the compression checks out but I'm not sure if I trust him cause he pulled the distributor and put it back in out of time. This weekend I'm testing compression and hope it's not a warped head or blown gasket. Still have to test the TPS so I have a few trails to run down.

Do the computers go out on those early jeeps often?

 

The ecu can be an issue, the head issues wouldn't cause it not to start just run like crap.

 

It's getting spark at all 6 plugs? What's your fuel pressure at? What's compression in all 6 hamster holes? Lets get some actual numbers here.

 

Spark is strong on all 6, fuel pressure is between 32-34 psi with the key on and upwards of 40 psi when cranking. Compression on the cylinders are between 120-150 psi. I took off the throttle body and the idle air control valve that had a bunch of soot on it and took off the TPS. Didn't have time to run to the parts store to get new sensors so I cleaned them and put it all back in.

I then tried to start the rig and it was sputtering which is a improvement but still didn't start. Then I pulled my fuel filter. The gas looked crappy (to be expected since it sat for 2 years). This weekend I'll change out both sensors and the fuel filter with clean fuel.

 

It could also be a crankshaft position sensor. I had this problem also

 

That's already been replaced, thanks though